Vehicles typically include an exhaust gas recirculation (EGR) system to selectively direct internal combustion engine exhaust gas to an air inlet of the engine. EGR can lower the level of certain undesirable engine emission components such as nitrogen oxide (NOx) and can improve fuel economy. Up to a limit, NOx emissions decrease with increasing EGR levels. Beyond the limit, EGR can increase formation of other undesirable engine emission components and can reduce vehicle drivability.
EGR typically involves recirculation of exhaust gas through an EGR passage between an engine exhaust conduit and an engine fresh air intake passage. A valve within the EGR passage (the EGR valve) is controlled to vary a restriction within the EGR passage to regulate the flow of exhaust gas therethrough. When EGR is not required, the EGR valve is driven to a full restriction (closed) position, typically through a spring preload. The spring preload is commonly required to be substantial to ensure rapid closing of the EGR valve when necessary, and to ensure proper sealing of a closed EGR valve. When EGR is required, the EGR valve is driven to an open position through application of a position control signal to an actuator mechanically linked to the EGR valve. The degree of opening of the EGR valve varies with the magnitude of the position control signal. When the EGR valve is open, recirculated exhaust gas enters the fresh air intake passage and flows to the engine cylinders.
Some vehicles also include a secondary air injection (SAI) system. It is known practice to run the engine in a fuel rich condition at start up to (a) aid in the operation of the cold engine and (b) provide fuel for reaction in the exhaust path downstream of the engine to quickly heat up the vehicle's catalytic converter. The SAI system includes an air pump to pump atmospheric air through an SAI passage and into the exhaust path downstream of the engine to react with fuel in the fuel rich exhaust during the time period immediately following vehicle start up. The reaction of the fuel rich exhaust and the pumped-in air, referred to as secondary or supplemental air, is exothermic and serves to heat up the catalytic converter. A valve is configured to selectively provide fluid communication between the air pump and the exhaust path.